The conference will bring together the leading investigators in the field of micronutrients and immunity and provide a synthesis of the current views of the topic. Beginning with the demonstration in the early 70's that protein-energy malnutrition impairs immunocompetence, recent work has highlighted the role of individual micronutrients, including vitamins and trace minerals, in optimum functioning of the immune system. It has been shown that zinc deficiency leads to increased risk of infection, which is mediated largely by impaired function of T lymphocytes and polymorphonuclear leukocytes. The findings are illustrated by changes in the immunocompetence of infants with acrodermatitis enteropathica. Copper deficiency impairs cell-mediated immunity and reticuloendothelial system. Vitamin A deficiency decreased lymphocyte responses in vitro and alters the integrity of epithelial barriers. Vitamin B6 has profound effects on cellular immunity and natural killer cell functions. Much of the data has been confirmed and extended by carefully controlled studies in laboratory animals. The animal models of single nutrient deficiency show increased susceptibility to a variety of infections. This is due largely to reduced immune responses. In many instances, the lymphoid organs show significant atrophy and reduced number of lymphoid cells. Mitogen responses are decreased and natural cell (killer) activity is decreased. Challenge with microorganisms or tumour cells confirms reduced immunocompetence. Serum thymic factor activity is reduced, particularly in zinc deficiency. These changes in immunity in micronutrient deficiencies (and excesses) have important clinical and public health significance.